This invention relates to fingerprint sensors and more particularly to apparatus and methods for managing power consumption in fingerprint sensing circuits and also to apparatus and method for detecting finger activity with fingerprint sensing circuits.
Power management is increasingly important in today's mobile electronic devices as greater reliance is placed on batteries and other mobile energy sources. This is true for devices such as portable computers, personal data assistants (PDAs), cell phones, gaming devices, navigation devices, information appliances, and the like. Furthermore, with the convergence of computing, communication, entertainment, and other applications in mobile electronic devices, power demands continue to increase at a rapid pace, with batteries struggling to keep pace. At the same time, even where additional features and capability are provided in modern electronic devices, consumers still desire elegant, compact devices that are small enough to be slipped into a pocket or handbag.
While power management continues to increase in importance, access control is also becoming increasingly important as it relates to modern electronic devices. Access control generally refers to methods and techniques for restricting the ability of a user or program to access a system's resources. Access control is gaining importance at least partly because users are storing increasing amounts of private, sensitive, or confidential information on mobile electronic devices. The electronic devices themselves are also valuable. Thus, restricting access to these devices may provide an effective deterrent to theft or misappropriation by reducing the value of the devices for would-be thieves or resellers.
Although reusable passwords are probably the most common technique for authenticating and identifying a user of a device, various other techniques are also being developed to counter the various ways that reusable passwords may be compromised. For example, fingerprint sensors provide one potential method for identifying and authenticating a user. Fingerprints, like various other biometric characteristics, are based on an unalterable personal characteristic and thus are believed to more reliable to identify a user. Nevertheless, like other features, fingerprint and other biometric sensors typically require additional hardware and software for implementation in electronic devices. This hardware and software adds to the already large power demands being placed on these devices.
In view of the foregoing, what are needed are apparatus and methods for efficiently managing and conserving power in fingerprint sensing circuits. For example, apparatus and methods are needed to significantly reduce power consumed by fingerprint sensing circuits when the circuits are idle or waiting for a user to apply a fingerprint. Further needed are methods and techniques to enable fingerprint sensors to quickly “wake up” when finger or non-finger related activity is detected by the circuit. Further needed are apparatus and methods for determining whether a finger is or is not present on a fingerprint sensor when detection begins.